LDV measurements in a Navy CPS fan

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Abstract

New ventilation fans for Navy ships need to filter
chemical agents from the supply air. This requires much
greater pressure ratios than in earlier fans. This research
was conducted to understand the performance of these new fans.
LDV measurements of axial and tangential velocities were
made in a Navy fan from upstream stations, throughout the
blade row, and downstream into the stator. Data were
collected two ways: (1) averaged over the entire rotor cycle
and (2) averaged at each rotation angle.

Upstream bimodal probability densities of the axial
velocity component were found in the cycle-averaged data.
Bimodal distributions indicate instabilities in the stagnation
or separation lines or vortex shedding. The phase-averaged
data show there to be a dependency of velocity on rotor
positions.

Downstream profiles mapped the large separation region
downstream of the rotor. The downstream region shows
recirculating flow and reattachment as the flow moves into the
stator section.

Phase-averaged profiles in the stator inlet plane show
the periodic rotor wake as it enters the stator. The
resulting flow angle does not match the stator angle.
In the blade row, the phase-averaged velocity profiles
show negative tangential velocit s near the leading edge and
separation occurring near midchord. The region influenced by
the separation extends across most of the blade passage as the
fluid approaches the exit plane of the rotor. The separation
in the blade row contributes to the poor performance of the
fan and low pressure recovery.